In most residential and industrial areas, some services make use of infrastructural networks such as telephone wires, heating gas pipelines and sewage ducts which run underneath the paved surfaces.
These networks require wells commonly referred to as manholes which allow both drainage of the surface and access to the infrastructural for inspection and maintenance operations.
Conventional manholes have a cover closing off their upper portion. The cover typically rests on an annular leveling base.
The cast iron frame has an annular recess adapted to support the base surface of the cover and to form a rim around the peripheral surface of the cover. During the initial paving operations of the surface surrounding the manhole, the supporting frame is positioned of top of the leveling base and asphalt is poured around the frame until the freshly covered pavement is level with the upper surface of the rim. Once the asphalt is dry, the upper surface of the rim, the upper surface of the cover and the pavement are all of the same level.
As the pavement periodically becomes worned out by the passage of vehicles and changes in temperature, it is customary to repair the damages by covering the old surface with a new layer of asphalt.
When such an operation is performed, it becomes necessary to raise the manhole cover to the level of the newly covered surface. Instead of completely rebuilding the concrete leveling base, it is common practice to use a raising structure positioned on the cover at the level of the new layer of asphalt.
These raising structures are also adapted to compensate the manufacturing defaults and normal wear which cause the upper surface of the cover to deform and to deviate from an horizontal plane even if the base of the cover is horizontal.
When the upper surface of the cover is no longer horizontal it is imperative that the rim which surrounds the cover be adjusted so that the upper surface of the rim is flush with the upper surface of the cover, all around its periphery. If a portion of the upper surface of the cover is not flush with the upper surface of the rim, the cover which sits on an horizontal support will tilt upon passage of vehicles. The resulting movement of the cover will cause additional wear to its structure and create a noisy interaction with the rim.
The conventional raising structure consists of an annular base ring and a top annular ring kept in vertically spaced relationship by independant spacing legs. The base annular ring and a top annular ring have respectively an outer and an inner diameter substantially corresponding to the outer diameter of the cover. The base annular ring is adapted to sit on the conventional cast iron supporting frame instead of the cover and the cover to rest on the top annular ring. During the resurfacing operations, once the raising structure is positioned on the conventional cast iron supporting frame, and the cover is placed on the base annular ring, the new layer of asphalt is poured until it is substantially level with the top surface of the cover. The length of the spacing legs is such that the upper surface of the rim exceeds the height of the cover. The spacing legs consists of rectangular or substantially parallelogram-shaped tongues of metal, the upper edge of the tongue being welded to the top annular ring and the bottom of the tongue being welded to the base annular ring. The tongues are relatively thin and adapted to crease.
When the compacting roller passes over the portion of the rim exceeding the top surface of the cover, each leg is adapted to bend randomly and generally in a plane perpendicular to the largest side of the parallelogram until the rim becomes flush with the upper surface of the cover all around its periphery, thus compensating for structural defects on the upper surface of the cover.
One of the major drawbacks of conventional structures is inherent to the fact that the legs which bend randomly and sideways abut against the cover once they are bent. This random bending action can also cause a vertical misalignement between the top and base annular rings. To circumvent the above mentioned disadvantages, the present invention uses spacing legs having a predetermined weakness plane.